A sandwich, the classic and perhaps original fast food, comprises a filling which can be meat, jelly, salad, or virtually any other substance one would not normally eat with the hands, encased in bread so that the combination can be eaten neatly. The bread can either be in the form of two discreet slices between which the filling is held, or a single elongated piece such as of the pita or French type that forms a pocket to hold the filling.
In spite of the many different mixtures or materials usable as fillings, the actual making of a sandwich represents a major bottleneck in the production of this style of food, which otherwise is very suitable as a fast food. Most sandwich fillings are wet and flowable, so that the sandwiches cannot be prefilled without making the bread soggy. Because of this and because different consumers want different sandwich garnishes, it is standard to make up sandwiches as they are ordered, something which requires experienced personnel if portions are to be uniform and quality high. Furthermore, if a certain filling should be heated, the purveyor must either keep a supply hot, which runs the risk of overcooking or otherwise ruining it, or heating up the individual batch, which further slows the transaction.